1. Field of the Invention
The present invention relates to a pattern exposure machine used in manufacturing a semiconductor integrated circuit and a LCD (liquid crystal display), and more specifically to a sample table for an X-ray exposure machine.
2. Description of Related Art
Recently, in order to elevate the integration density and the operation speed of the semiconductor integrated circuit, effort is continuously made to microminiaturize semiconductor device elements incorporated in the semiconductor integrated circuit. In addition, with microminiaturization of device elements, whether or not overlay precision between semiconductor device elements formed in various processes is satisfactory, has become very important. In ordinary cases, a required degree of the overlay precision is one-fourth to one-third of the size of the device elements. This means that, in a pattern formed by a recently developed 0.25 xcexcm rule or 0.18 xcexcm rule, the degree of overlay precision of 50 nm or 80 nm is required.
On the other hand, a silicon substrate used for manufacturing a semiconductor integrated circuit can slightly shorten (contract) or elongate (expand) because it is subjected to a heat change in a manufacturing process and because a thin film having an internal stress is deposited. For example, if a silicon nitride film having a thickness of 0.2 xcexcm is deposited on a silicon wafer having a diameter of 6 inches, the shortening of 4 ppm occurs, namely, a pattern having a length of 20 mm becomes short by 80 nm. This shortening of 80 mm is comparable to the above mentioned required degree of overlay precision, and therefore, is a nonnegligible magnitude. Therefore, in a pattern transfer of a succeeding exposure process, it is necessary to conduct the exposure while compensating for the amount of shortening.
Furthermore, when an oxide silicon film having a thickness of 1.0 xcexcm is deposited on the silicon substrate by a CVD (chemical vapor process), the elongation of 5 ppm occurs, namely, the pattern having the length of 20 mm becomes long by 100 nm. This elongation of 100 nm exceeds the above mentioned required degree of overlay precision, and therefore, is also a nonnegligible magnitude. Therefore, in a pattern transfer of a succeeding exposure process, it is necessary to conduct the exposure while compensating for the amount of elongation.
In the meanwhile, in a light exposure machine for conducting a reduction transfer of a mask pattern by use of ultraviolet rays, it is possible to slightly modify a transfer magnification from a predetermined value by adjusting a lens interval in a lens assembly of an optical system. Therefore, the compensation required in the exposure process as mentioned above can be easily realized.
However, in an X-ray exposure using as a light source a synchrotron orbital radiation (SOR) which is effective in forming a fine pattern which cannot be formed in the light exposure using the ultraviolet rays, since there is no lens which can be effectively used for the X-rays, a mask having the magnification of xc3x971 is used. Therefore, it is impossible to change the magnification in the pattern transfer.
Under the above mentioned circumstance, Japanese Patent Application Pre-examination Publication No. JP-A-63-260023 (an English abstract of JP-A-63-260023 is available and the content of the English abstract of JP-A-63-260023 is incorporated by reference in its entirety into this application) proposes to change the temperature of both of a mask supporting member and a sample substrate so as to carry out the compensation required in the exposure process, by paying attention to the fact that the mask supporting member (fused quartz) and the sample substrate (silicon) have different expansion coefficients. This will be called a xe2x80x9cfirst prior artxe2x80x9d hereinafter.
Furthermore, A. C. Chen et al, xe2x80x9cMagnification correction for proximity x-ray lithographyxe2x80x9d, Proc. SPIE, Vol.2437, pp140-150, 1995 (the content of which is incorporated by reference in its entirety into this application) proposes to apply an external force to a mask support member so as to forcibly elongate the mask thereby to carry out the compensation required in the exposure process. This will be called a xe2x80x9csecond prior artxe2x80x9d hereinafter.
However, the first and second prior arts have the following problems:
In the first prior art, there is a variable factor of the machine itself caused by the temperature change of the mask supporting member and the sample substrate. Namely, the degree of precision lowers disadvantageously in a magnification deviation measuring means and in a position deviation measuring means. Furthermore, after the temperature is changed, a time of ten minutes to a few ten minutes is required until the temperature becomes stabilized, and therefore, the compensation amount cannot be modified for a short time.
In the second prior art, since it is necessary to apply the external force to the mask support member, the fatigue is liable to occur in the mask support member, and the mask itself or the mask support member is liable to be broken. In addition, since the external force is applied only in a direction of elongating the mask, application of the external force is limited to only the case that the pattern formed on the sample is larger than the mask pattern. In other words, it is impossible to comply with the case that the pattern formed on the sample is smaller than the mask pattern.
Thus, in order to carry out the adjustment for a short time for the purpose of meeting with the expansion of the sample silicon substrate, the application of the external force is more advantageous than the changing of the temperature. However, in the application of the external force to the mask support member, the mask itself or the mask support member is liable to be broken.
Accordingly, it is an object of the present invention to provide a sample table for a pattern exposure machine, which has overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a sample table for a pattern exposure machine, effectively used particularly in an X-ray exposure machine, capable of precisely matching the pattern already formed on a sample substrate with a mask pattern by applying an external force to the sample substrate.
The above and other objects of the present invention are achieved in accordance with the present invention by a sample table for use in a pattern exposure machine configured to transfer a circuit pattern formed in a mask onto a sample, the sample table being so constructed that the sample is placed on the sample table, the sample table being divided into a center part and a peripheral part surrounding the center part, the sample table comprising a means for radially displacing at least a portion of the peripheral part in a condition that the sample is attracted to the sample table.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.